1. Field of the Invention
The present invention relates to a fastener for opposing uplift forces in light framed construction.
2. Description of the Related Art
In construction such as residences, small buildings, multi-family and other light-framed construction, an uplift restraint system typically includes uplift resisting connectors at the roof to top of a wall, top of a wall to vertical studs, vertical studs between adjacent floors and to the foundation. Winds and other external forces may generate upward loads on framing members. In order to counteract these upward loads, the framing members may be anchored to the surface on which they are supported. On the ground level, anchor rods are typically sunk into a concrete foundation, and the bottom plate of the wall is bolted to the anchor rods. For levels built on top of the first level, straps are often used to anchor the upper level to the level below. FIG. 1 is a perspective view of an upper level 30 anchored to a lower level 20 via a coil strap 40 in a light framed construction. While only one anchor strap is shown affixed to a pair of aligned studs 22 and 32 on the adjoining levels, coil straps may be provided in each pair of aligned studs in the respective levels to anchor the level 30 to the level 20.
Prior art FIG. 1 shows a stud 22 and top plates 24 and 26 from lower level 20. A stud 32, bottom plate 34, subflooring 36 and floor joist 38 are shown from upper level 30. Nails or other fasteners may be provided along the length of coil strap 40 (at least in the portions overlapping the lower stud 22 and upper stud 32) to fasten the coil strap 40 to the upper and lower levels. A typical coil strap 40 may be formed of various thicknesses including 16 gauge steel, such as for example the CS16 coil strap by Simpson Strong-Tie Company, Inc. of Pleasanton, Calif.
While effective at anchoring upper levels to lower levels, coil straps have certain drawbacks. First, they need to be positioned on the exterior of a framed construction, and require scaffolding or other support mechanisms to allow workers to install the coil straps. Second, the vertical studs must align on adjacent floors for strapping to be installed. Third, the wooden members in a framed construction, including the top and bottom plates, floor and rim joists, settle or compress during to the load of the structure and shrink over time. Shrinkage in lumber occurs as the moisture in the wood members evaporates causing the members to constrict. This constriction may result in buckling or bowing outward of the strap, as well as any siding or exterior covering of the framed construction.